The invention relates generally to throttle control systems for two-cycle engine drive hand-held blowers and, in particular, to throttle control systems for hand-held blowers in which the throttle lever is positively indexed at small incremental angles.
Existing low cost hand-held blowers use throttle control levers mounted directly to the throttle shaft, and they typically have three settings: Closed, Idle, and Wide Open Throttle (WOT). The throttle positions can be described as an angular rotation of the handle about the shaft from the Closed position. For example, in existing blowers, the throttle position at the Idle setting is approximately 35xc2x0 from the Closed position.
An optimum fuel ratio is the fuel-air mixture that will achieve the highest engine speed (measured in revolutions per minute, or RPM) at a given throttle setting. For an optimum fuel mixture and a throttle position of 35xc2x0 (the current Idle position), the speed of the blower would be too fast. Previous blowers lowered their Idle speed by increasing the fuel ratio at the Idle position. A fuel-rich setting causes inefficient combustion, which in turn lowers the Idle speed; however, the fuel-rich setting also increases emissions from these blowers. Because of new emissions regulations for hand-held blowers specifying that idle emissions account for 15% of the total emissions limit, fuel mixtures cannot be set as rich as they have previously been.
When the fuel mixture is set at the optimum level, the speed of the blower for a given throttle opening will increase. The blower""s Idle speed can be lowered by setting the Idle position so that throttle opening is less open. Whereas fuel-rich blowers had an Idle position at around 35xc2x0, blowers having an optimal fuel ratio must have an Idle position in an approximate range of 4xc2x0 to 14xc2x0 (preferably, 10xc2x0 to 14xc2x0) to maintain an appropriate Idle speed, approximately 4000 RPM.
But existing throttle controls cannot hold the throttle at such a small open position. It is desirable for a throttle to xe2x80x9csnapxe2x80x9d into place as it moves between positions. To achieve this desired feel, existing throttle controls use a spring-loaded steel ball in the carburetor body that falls into a drilled detent in the throttle shaft. Because of the small shaft diameter and the size of the steel ball, the detents corresponding to the Stop and Idle positions would overlap too much to function effectively.
The present invention is directed to throttle control systems for carburetors.
In accordance with one embodiment of the invention, a throttle control system for a carburetor comprises a throttle valve, a throttle valve shaft rotatably received in the carburetor, a throttle lever, and a detent. The throttle lever comprises an arm and a hub, the hub formed by an annular recess circumscribed by an annular rim, wherein notches are formed on the inside of the annular rim. The detent comprises an annular hub and a flexible arcuate arm extending about a portion of the hub, and from the arcuate arm extends a protrusion shaped to mate with the notches of the throttle lever hub. The detent is piloted over the throttle valve shaft and fixed to or captured relative to the carburetor, and the throttle lever is fixed to the throttle valve shaft so that the detent is at least partially located within the lever hub annular recess. As the throttle lever is rotated with respect to the carburetor, the notches of the throttle lever hub move with respect to the protrusion of the detent, and when one of the notches indexes the protrusion, the protrusion mates with the notch, thereby positively indexing the lever.
In accordance with another aspect of a preferred embodiment, the annular rim of the throttle control lever has at least two notches located within an arc distance of 14xc2x0 along the annular rim. In accordance with another aspect of a preferred embodiment, the throttle lever includes a stop that prevents the lever from being rotated past one or both of the Closed or WOT positions.
In accordance with another aspect of the preferred embodiments, a mechanism for making minor adjustments to the idle position of the carburetor is provided. Provided is a first member moveable with respect to the detent in a first direction to contact the rigid arm, and further moveable in the first direction to displace the rigid arm in a second direction substantially transverse to the first direction, thereby causing the flexible arm to bend and the detent to rotate relative to the carburetor. This changes the angular position at which the detent indexes the throttle lever, thus slightly changing the idle state of the carburetor. This mechanism also allows for variations of the idle states that arise from manufacturing tolerances to be fixed.
Implementing the detent on the throttle valve shaft has several advantages over implementing it remotely from the shaft. By keeping the detent means close to the throttle valve shaft, xe2x80x9cplayxe2x80x9d in the system is minimized and the performance of the control system is thus improved. This leads to more accurate positioning and, ultimately, to a better user feel when accessing the throttle positions. Further, control systems implemented remotely from the carburetor are less reliable than systems that implement the system in the carburetor.
Other aspects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.
FIG. 1 is an exploded assembly view of the carburetor, throttle valve shaft, throttle lever, and detent according to a preferred embodiment.
FIG. 2 is a bottom view of the throttle lever.
FIG. 3 is a top view of the detent according to a preferred embodiment.
FIGS. 4a-c are bottom views of the throttle lever and detent assembly as the lever is rotated to engage the detent in the Closed, Idle, and WOT positions, respectively, according to a preferred embodiment.
FIG. 5 is an exploded assembly view of the carburetor, throttle valve shaft, throttle lever, and detent according to another preferred embodiment.
FIG. 6 is a top view of the detent according to another preferred embodiment.
FIG. 7 is a side view of the detent of FIG. 6.